High speed tenter frame



Jan. 20, 1970 J. F. PFEFFER, JR

HIGH SPEED TENTER FRAME 2 Sheets-Sheet 1 Filed March 25, 1968 IN VEN TOR PFEFFER, JR.

JAMES F.

a F 5 13 W M, i, x;

ATTQRNEY Jan. 20, 1970 J. F, PF'EFFER, JR

HIGH SPEED TENTER FRAME 2 Sheets-Sheet 2 Filed March I25 1968 INVENTOR PFEFFER, JR

JAMES A 1 1 ORNEY United States Patent Ofiice 3,490,094 Patented Jan. 20, 1970 3,490,094 HIGH SPEED TENTER FRAME James F. Pfeffer, Jr., Newark, Del., assignor to E. I. du

Pont de Nemours and Company, Wilmington, DeL, a

corporation of Delaware Filed Mar. 25, 1968, Ser. No. 715,791 Int. Cl. B29c 17/02 US. Cl. 181 4 Claims ABSTRACT OF THE DISCLOSURE An improved tenter frame apparatus for transversely stretching thermoplastic film wherein diverging and converging grooved joints provide for smooth translational motion of the tenter chain and guide blocks as they pass the change-of-direction sections of the tenter frame on the tension side of the rail.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to apparatus for stretching webs and more particularly it relates to an improved tentering machine.

Description of the prior art Tentering frames are commonly employed in web treating processes of the textile and thermoplastic film manufacturing industries. Such frames form endless guides for chains which convey guide blocks upon which the tentering clips are mounted. The tentering clips grasp the edges of the webs being treated and convey these webs through the tentering operation.

Thermoplastic film is commonly stretched in the transverse direction by use of such tentering means. The equipment normally has a pair of tenter frame rails which, in part, has a divergent section so that the path of the tentering clips which grip the web being conveyed effects an extension in the transverse direction of the web. Such frames have at least one frame joint which divergently guides the chain, guide blocks and tentering clips and another converging frame joint which returns the chain path to a direction parallel to the path of the conveyed web. The angular change in the rail configuration made by these joints is dependent on the initial width of the web being processed and the desired degree of stretching.

The design of these changeof-direction tenter frame sections limits the operational speed of the chain and blocks which convey the tentering clips. Change-of-direction joints that have discontinuous boundaries, sharp corners or small radius bends for guiding the chain and blocks cause high local loads and cause the lubricant to be scraped from the wear surfaces of the chain blocks as they pass and abut these discontinuous boundaries. This causes excessive wear and limits the life of the chain blocks. Compensation for this condition is often made by over lubricating the chain and grooved rail channel. This procedure results in a significant increase in the required driving motor horsepower, is wasteful of lubricant and creates adverse product quality defects due to the proximity of the excess lubricant to the web being processed. Additionally, the inertia forces of the chain at the change-of-direction sections while operating at speeds exceeding approximately 200 y.p.m. are such that the individual chain blocks are required to make a rapid pivotal motion causing the blocks to leave the abutting surface of the grooved frame channel and abut the opposing surface of the grooved frame channel. If either abutting surface is not uniform in transition from section to section continuous vibrations are generated which immediately become reflected in the web being processed. The efiecfs of these vibrations are evident in the form of ripples in the web and nonuniformity of the product. This condition is a major cause of web breaks during the stretching process and a major cause of equipment failure.

SUMMARY OF THE INVENTION According to the present invention there is provided in a tentering apparatus for stretching thermoplastic web material by use of tentering clips and providing a uniform distribution of transverse stretching forces comprising a frame, a pair of sectionalized grooved rails arranged in a closed loop path mounted on the frame, a pair of endless chains which are guided within chain channels formed by the grooves of the rails, tentering clips being conveyed by the chains, means for driving the chains in their closed loop paths within the grooved rails, and means for adjusting the sectionalized grooved rails within various degrees of diverging and converging relationship with respect to one another wherein the improved means for adjusting the sectionalized grooved rails comprises:

(a) at least one pair of diverging grooved joints with each joint comprising;

A first section of grooved rail whose grooves form the chain channels and are coextensive with the grooves of the adjacent section of sectionalized grooved rail, the grooves having a straight inner wall,

A second section of grooved rail whose grooves form the chain channels and are coextensive with the grooves of the first section of sectionalized grooved rail, the grooves having a straight inner wall,

A fixed stub shaft journal whose axis is vertically located on the non-web side of the grooved rail,

A first bearing connected to the first section of grooved rail mounted for partial rotation around the fixed stub shaft journal,

A second bearing connected to the second section of grooved rail mounted for partial rotation around the fixed stub shaft journal,

A two-part curved inner wall on the chain channel on the web side of the rail arranged so that one part is afiixed to the second section of grooved rail and coextensive with the corresponding straight inner wall of the second section and the other part is aflixed to the first section of grooved rail and coextensive with the corresponding straight inner wall of the first section, each part having a curved section at its detached end to slideably engage the other on a common curvilinear plane at a fixed radial distance from the fixed stub shaft journal,

A cross-slide terminating in the fixed stub shaft journal, and

Means to move the cross-slide in a transverse direction; and

(b) at least one pair of converging means to converge adjacent sections of the sectionalized grooved rails with the converging means having a continuous flexible outer wall on the chain channel on the web side of the rail, the outer wall being used to guide the chain.

BRIEF DESCRIPTION OF THE DRAWINGS Reference to the following drawings will facilitate the understanding of this invention.

FIGURE 1 is a partial schematic plan view of the tenter frame rails.

FIGURE 2 is a typical cross-sectional view of the chain channel taken at Section 22 in FIGURE 1, additionally showing the chain, a chain guide block and a tentering clip positioned within the chain channel.

FIGURE 3 is a plan view of the diverging rail joint.

FIGURE 4 is a plan view of the converging rail joint.

FIGURE 5 is a top schematic view of the channel wear 3 str ip employed in the convergingrail joint embodiment shown in FIGURE 4.

FIGURE 6 is a plan view of another embodiment of a converging rail joint using the same type of wear strip as shown in FIGURE 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The apparatus of this invention comprises two types of change-of-direction joints for a tenter frame with each joint having an effective long-radius pivoting point from which the movement of the active wear surface within the grooved rail on the load side is controlled.

One type of change-of-direction joint provides for diverging adjustment of the rails and the other type provides for converging adjustment of the rails. Each type of joint insures translational motion for the chain blocks as they change their direction within the chain channels on the tension side of the chain.

The diverging joint has a two-part wear strip forming the non-web side wall of the chain channel on the tensioned side of the rail. This wear trip abuts the rear surfaces of the chains guide blocks thereby guiding them in a manner to permit translational motion of the guide blocks as they pass through the joint. The two-part wear strip is designed to assure a continuous abutting surface for the chain blocks when the joint is partially rotated. This design comprises a straight Wear strip terminating in a curved configuration with a radius of curvature at a fixed distance from the diverging joints pivot point and a curved wear strip having a radius of curvature of approximately 40 inches which has an end terminating with a radius of curvature corresponding to that of the straight wear strip and arranged so the two wear strips continually abut one another as the joint is partially rotated.

The converging joint provides for translational motion of the chain blocks as they assume a path of travel substantially parallel to the direction of the path of the web being processed. This joint has a single-piece flexible wear strip forming the web side wall of the chain channel on the tension side of the rail for guiding the guide blocks of the chain in a converging path. This wear strip abuts the front surfaces of the guide blocks to achieve the desired translational motion of the blocks as they pas-s through the converging joint. The single-part wear strip has an adjustable minimum effective radius of curvature of approximately 200 inches and is designed to flex with the movement of the joint as it is operated.

This apparatus when used with grooved tenter frame chain channels permits thermoplastic film to be stretched in the transverse direction at film speeds in excess of 200 yards per minute without causing rippling of the web being processed and with a reduced break frequency during the processing.

Additionally the use of the apparatus of this invention results in reduced maintenance costs on the chain, chain guide blocks and chain clips because such equipment is subjected to less vibration and less metal-to-metal engagements than it is when used with conventional tenter frame equipment.

Referring to FIGURE 1 the tenter frame comprises a lefthand frame rail 11 having straight rail sections 12, 13,j15,,and 16, a right-hand tenter frame rail 17 having straight rail sections 18, 19, 20 and 21, main drive sprockets 22 and 23, idler sprockets 24 and 25, chain tensioning hydraulic cylinders 26 and 27, diverging rail joints 28 and 29, converging rail joints 30 and 31, transition pivots 32 and 33, cross-slides 34, 35, 36, 37, 38, 38a, 39 and 39a and mechanically driven adjusting screws 40, 41, 42 and 42a. The paths of the tenter frame chains within the grooved chain channels are shown by the broken lines 43 and 44. In this particular preferred embodiment only two diverging joints 28 and 29 and two converging joints 30 and 31 are employed. The generic 4 design is not so limited, however. A plurality of pairs of each of such joints could be employed if the desired web transverse stretching pattern requires greater degrees of divergence and/or convergence than are achievable by use of single pairs of joints as shown in FIGURE 1.

The left-hand and right-hand tenter frames 11 and 17 are adjustable transversely by the driven adjusting screws 40, 41, 42 and 42a and by similar adjusting screws, not shown, at the entrance end of the tentering apparatus shown in FIGURE 1. These adjusting means provide flexibility in rail separation to accommodate the particular desired stretching pattern to be imposed on the web being processed.

FIGURE 2 is a typical cross-sectional view of the groove chain channel 45 such as taken at Section 2-2 in FIGURE 1 with the addition of the tenter chain, a chain guide block and a tenter clip in a typical operating position within the grooved chain channel. The chain channel 45 accommodates the tenter chain 46 which is driven by the sprocket 22 along the path 43 as previously shown in FIGURE 1. A chain guide block 47 such as described in US. Patent 3,118,212 is mechanically connected to the chain 46 and is used to guide the chain along the paths 43 and 44. A web tentering clip 48 is mechanically connected to the guide block 47 which is employed to grip the web 14 being processed as shown at 49. Wear strips 50 and 51 and block guides 52 and 53 are attached to the tenter frame rail section 13 and provide the closed path in which the chain guide blocks, such as guide block 47, travel while subjecting the film web to the transverse loading forces required to effect the desired degree of stretching.

The salient feature of this invention resides in the apparatus which provides for smooth continuity of the wear strips, such as 50 and 51, to assure continuous abutment for the guide blocks as they proceed through a change-ofdirection path within their closed-loop travel.

FIGURE 3 is a plan view of the diverging rail joint 29 shown in FIGURE 1 showing in greater detail the means for achieving the smooth transition of the wear strips of the chain channel on the tension or load side of the rail between the straight rail sections 18 and 19. The diverging rail joint shown in FIGURE 3 has two operable sections 54 and 55 to which bearings, such as 54a, are connected. These bearings pivot about the common stub shaft journal 56 which is actuated by the driven adjusting screw 40 shown in FIGURE 1. The operable section 54 is mechanically attached to straight rail section 19 while the operable section 55 is mechanically attached to the preceding straight rail section 18. The chain channels on the tension and slack side of these operable sections are coextensive with the corresponding chain channels of the straight rail sections to which they are mechanically attached. The chain channel on the tension side of the rail has a continuous outer wear strip on its Web side wall, at the change-of-direction location, formed by wear strips 57 and 58 which interlock with one another when the diverging joint 29 is operated. The average radius of curvature of these wear strips is relatively large, such as from 40 inches to 200 inches, in order to keep the combined force resulting from film tension, the centrifugal forces and the forces resulting from the chain tension at a desired level. The interlocking wear strips 57 and 58 normally do not control the movement of guide block 47 shown in FIGURE 2, since sufiicient tension is set on the chain to insure that block 47 rides against mating wear strips 51a and 51]). These strips only control such movement during an emergency loss of chain tension. A two-part curved inner wall opposing the web side wall on the tension side of the rail is also continuous and is formed by mating wear strips 51a and 51b. The vertical cross-section of these strips is as shown by the composite of sectioned parts 51, 52 and 53 in FIGURE 2. The surface of wear strip 5112 which engages with the surface of wear strip 51a shown in FIGURE 3 is at a constant radial distance from the centerline of stub shaft journal 56. It is preferred that this radial distance be about 40 inches so that with proper chain tension the loading force always is against the wear strips 51a and 51b due to the tension imposed on the chain. The guide blocks such as 47 shown in FIGURE 2 that are used with this design of chain rail have a shaped surface designated by 59 in FIGURE 2 to conform to the curvature of wear strip 51b. It is at these diverging joints only where the surface 59 of guide block 47 abuts a wear strip that there is a no-clearance configuration. It is for this reason that the curvatures of wear strip 51b shown in FIGURE 3 and the guide block surface designated as 59 in FIGURE 2 are of equal geometric proportions. This prevents lineal contact from occurring at the diverging joints which would remove lubricant from between these surfaces and would result in high loads causing wear and in vibratory motion of the guide blocks as they proceed past these change-of-direction paths. Since the recessed groove surface is continuous for any setting within the rotational design limitations of the diverging joint and since the surfaces of the guide blocks which abut the recessed grooved surface are of the same curvature, the movement of the chain guide blocks through the diverging joints is smooth and vibration-free.

FIGURE 4 is a plan View of the converging rail joint 31 shown in FIGURE 1 showing in greater detail the means for achieving the smooth transition of the wear strips on the load side of the grooved chain channel between the straight rail sections 19 and 20. The converging rail joint shown in FIGURE 4 is supported from the pivotal center support 60 which pivots about stub shaft journal 61. Stub shaft journal 61 is connected to the cross-slide 37 shown in FIGURE 1 which is actuated by use of driven adjusting screw 41. In the preferred embodiment shown in FIGURE 4 the converging joint 31 is pivotally secured to the adjacent straight rail sections 19 and by pivots 62 and 63. A mechanical linkage comprising a pivot center 64 which is fixed to straight rail section 20, a pivot center 65 which is fixed to straight rail section 19, straight links 66 and 67, toggle link 68 having a shaft extension 69 and mating socket 70 fixed to the converging joint 31 automatically and equally distributes the angular motion at pivots 62 and 63 as the converging joint 31 is moved transversely by the movement of stub shaft journal 61.

To transmit the transverse loading forces to the Web being processed via the web tentering clips the grooved chain channel on the tension side of the rail has smooth continuous walls within the converging joint through which the tensioned chain and its guide blocks travel. The inner wall of this channel is formed by wear strips 51, 53 and 71. The movable portion of the wear strip designated as 71 engages the adjacent straight line rail sections at radial surfaces designated at 72 and 73. Radial surface 72 rotates about pivot 63 while radial surface 73 rotates about pivot 62. In operation clearance exists between wear strip 51 and the rear surfaces of the guide blocks such as designated by 59 in FIGURE 2. The opposite surfaces of the guide blocks 59a abut the outer wall of the chain channel formed by wear strip 50a as they pass through the converging channel of converging joint 31 on the film side of the joint. Wear strip 50a is bolted to the converging joint 31 so that the portion of the wear strip which passes through the joint is fixed to the joint. The ends of the wear strip 50a are slideably attached to the adjacent straight rail sections 19 and 20 and engage these adjacent straight rail sections by a radial and tongue-and-groove engagement. This permits the overlapping portions of the wear strip 50a to be flexed upon adjustment of the converging joint 31 and to be subjected to a simple bending movement when so flexed.

FIGURE 5 is a top schematic view of wear strip 50a showing its construction in greater detail. The wear strip section A is the portion that is rigidly bolted to the converging joint. This section preferably has a radius of curvature of 200 to 300 inches in order to minimize the forces on the guide blocks resulting from the combined forces from film tension, the centrifugal forces and the forces resulting from chain tension as the chain passes through the converging joint channel. In the straight section the load of the film stretching force is transmitted through surface 59a shown in FIGURE 2 to the chain channel via the surface of wear strip 50. Both these surfaces are flat and carry the loads without significant wear if they are properly lubricated. At the converging joint shown in FIGURE 4 the flat surface 59a must contact the curved surface 50a. By using a large radius and adequate lubrication an oil film is developed for distributing this load in other than a lineal distribution. Sections B and C are the portions of the wear strip which flex when the converging joint is adjusted. It is preferred that these sections have a minimum radius of curvature of approximately one-half of that of section A. The value of the radius varies as the angle changes. As shown in FIGURE 5, sections B and C are undercut to permit this degree of flexing when subjected to loading. These sections specifically bridge the openings between the straight rail sections 19 and 20 and the converging joint 31. The portions of the wear strip 50a which extend beyond sections B and C are straight sections. These are provided with slotted bolt holes so that the wear strip ends can be slideably secured to the straight rail sections 19 and 20. Additionally, the wear strip has tongues 74 and 75 machined on its ends which engage grooves in the adjacent wear strips of the straight rail sections 19 and 20 so that lineal motion takes place at the end portions of the wear strip as the strip is flexed.

FIGURE 6 shows a plan view of an additional embodiment of a converging joint which employs the same design principles as used in the preferred embodiment shown in FIGURE 4. This embodiment is of simpler construction and 1s adequate when a lesser angle of convergence is required than that of which the FIGURE 4 configuration is capable. As shown in FIGURE 6 the stub shaft journal 76 serves both as the pivotal attachment between the adacent straight rail sections and as the actuating pivot about which the joint operates. The wear strip 77 in this embodiment is similar in design to that of the wear strip shown in FIGURE 5 with the exception that it is capable of bridging but a single opening at its flexing section. The salient feature of this joint is the same as that of the joint shown in FIGURE 4 wherein the wear strip 77 remains smooth and continuous during the flexing of the joint which provides for vibration-free passage of the guide blocks as they pass by and abut the wear strip 77.

What is claimed is:

1. In a tentering apparatus for stretching thermoplastic web material by use of tentering clips and providing a unlform distribution of transverse stretching forces comprising a frame, a pair of sectionalized grooved rails arranged in a closed loop path mounted on the frame, a pair of endless chains which are guided within chain channels formed by the grooves of the rails, tentering clips, being conveyed by the chains, means for driving the chains in their closed loop paths within the gooved rails, and means for adjusting the sectionalized grooved rails within various degrees of diverging and converging relationship with respect to one another wherein the improved means for adjusting the sectionalized grooved rails comprises:

(a) at least one pair of diverging grooved joints with each joint comprising;

a first section of grooved rail whose grooves form the chain channels and are coextensive with the grooves of the adjacent section of sectionalized grooved rail, said grooves having a straight inner wall,

a second section of grooved rail whose grooves form the chain channels and are coextensive with the grooves of said first section of sectionalized grooved rail, said grooves having a straight inner Wall,

a fixed stub shaft journal whose axis is vertically located on the non-Web side of the grooved rail,

a first bearing connected to said first section of grooved rail mounted for partial rotation around the fixed stub shaft journal,

a second bearing connected to said second section (b) bearing means located between the grooves of adjacent rail sections and rotatively connected to said stug shaft journal for partial rotation thereabout, and

(c) means to move said cross-slide in a transverse direction.

3. The tentering apparatus of claim 1 wherein said converging means comprises:

(a) a cross-slide having a vertical stub shaft journal, (b) a separate grooved rail section having a centrally located hearing which is rotatively connected to said of grooved rail mounted for partial rotation 10 around the fixed stub shaft journal, stub shaft journal for partial rotation thereabout,

a twopart curved inner wall on the chain channel (C) pivots terminally located between the separate on the web side of the rail arranged so that one grooved rail section and its adjacent rail sections, art i affixed to the econd ection of grooved (11) means to equalize the movement of said pivots rail and coextensive with the corresponding 15 in response to movement of said cross-slide stub straight inner wall of the second section and the aft journal, other part i fli d t h fi t ti of (e) means to move said cross-slide in a transverse grooved rail and coextensive with the c rreti n, and di i h inner ll f th fi t ti (f) slide means in each of the grooved rail sections adeach part having a curved section at its dejacent to said separate grooved rail section arranged tached end to slideably engage the other on a so that said continuous flexible outer wall is slideahly common curvilinear plane at a fixed radial g ged With the corresponding outer walls of the distance f h fi d b haft j L adjacent sections while the outer wall of the converga cross-slide terminating in said fixed stub shaft ing loint is biI1gfl6Xi j L d 4. The tentering apparatus of claim 3 wherein said with said converging means having a continuous flexible outer wall on the chain channel on the web side of the rail, said outer wall being used to guide the chain.

pivots are located equidistantly from said centrally located bearing.

4/1965 Nash. 4/1965 Nash.

WILLIAM J. STEPHENSON, Primary Examiner 2. The tentering apparatus of claim 1 wherein said converging means comprises:

(a) a cross-slide having a vertical stub shaft journal,

US. Cl. X.R. 

